mechanism, the rider is exerting, let us say, a force of twenty pounds, ten pounds on the fore hand to maintain the "in hand," and ten pounds with the legs, to maintain the contact with the bit. Otherwise the "in hand" will cease and the state of equilibrium be lost.
Suppose, now, that, in order to send the horse forward at a walk, the rider, keeping always the pull of ten pounds at the reins, increases the pressure of his legs to fifteen pounds and then to twenty; but the horse still keeps its center of gravity where it was, and remains standing still. If at this point the rider gives the hand, the center of gravity will pass forward and the horse will start; but the "in hand," which is part of the equilibrium, will be lost. If, therefore, the legs alone have not the power needed to push the center of gravity forward while the reins continue to act, the rider must have spurs with which to multiply their effect.
The horse having, if I may so express myself, let the center of gravity pass forward, would fall if it did not at once extend a fore leg to receive the weight. This constitutes one step. As the horse moves forward, the spurs abandon their contact; but the legs still maintain their pressure as before the spurs were applied. The center of gravity will return to the middle point; but the horse will continue to move forward, still in the state of equilibrium. All this is in accord with Newton's
